A bearing is a usual component of machinery. It is used for holding rotating or slipping parts and keeping them moving in the right position. Ball bearings used worldwide are too expensive to be applied to low cost products. Hence, the cheaper powder-sintered sleeve bearings play an important role in recent machine manufacturing. The conventional sleeve structure is shown in FIG. 1(a). A rotating shaft 1 is plunged into a through hole 12 of the bearing 13. A bearing stand 14 is engaged with the powder-sintered bearing 13 and a cavity 15 is formed at the bottom of the bearing stand 14. The cavity 15 is in communication with the through hole 12 and full of lubricant used for reducing friction forces between the rotating shaft 11 and the inward wall 16 of the bearing 13 due to high-speed rotation of the rotating shaft 11. High-speed rotation, however, causes the lubricant to flow out via the gap between the rotating shaft 11 and the inward wall 16. The heat generated by the high-speed rotation also causes evaporation of the lubricant. Reduction of the lubricant will make the rotating shaft 11 contact with the inward wall 16 of the bearing 13 directly as shown in FIG. 1(b). Greater friction forces thus incurred on the top part 17 and the foot part 18 of the bearing 13 will shorten the bearing life. The present invention is developed for the purpose of decreasing the leakage of the lubricant and avoiding direct contact between the rotating shaft and the bearing.